RE: CO meters (again)

[Tami Bond <yark@u.washington.edu>]

Crispin,

> I do have the capability to weight the entire stove to 2 grams and we do
> watch the fuel burn and the water temp rise. This is very good for the short
> time (3 or 4 mintes) until the water starts boiling and then it is a guess
> thereafter because some of the loss is water and some is fuel.

Bryan had lots of good ideas here (suspending pot etc). Another thing you
need is a measure of flow rate through your hood-- I assume you have a
hood collecting the exhaust. Since you are measuring the CO after the
stove exhaust has entrained some air, the concentration is affected by how
much dilution has occurred. To remove that effect, and to allow you to
calculate total CO emitted, you have to measure either volume flow rate at
the point of CO measurement, or CO2 at the point of measurement. (Another
way to do it, which has been discussed on this list, is to dump the
exhaust into a known volume. But this does not allow you to look at your
transients very well.)

Best thing to do is put a really light draft on the hood, like a little
blower. Is this possible? You need to make sure you are collecting all the
exhaust, but not provide enough draft to affect the combustion. Then you
have to measure the flow. The cheapest way I have found to do this is to
attach a 6" flow grid ($25) to a pressure transducer with an analog
output ($40). The flow grid gives you a better and quicker idea of flow
than a pitot tube traverse. Anyone have a better idea?

> As I want to measure the CO and CO2 from a cold stove being lighted (which
> is when the combustion is worst) I will have to have something that
> stabilizes in a lot less than 11 minutes becase that is three times as long
> as a typical test!

I agree with you and with Bryan that we want to know something about
transient operation and especially specific actions. We might get more
benefit out of working on specific combustion phases rather than the stove
as a whole.

Even if the response time refers to temperature and not CO, the long
response is a problem, because the temperature will change when you light
the stove. I am not sure, though, that another electrochem cell will fix
the problem. I wonder how much of a comparison between two sensors is
governed by one company being more honest or conservative than another,
rather than actual performance. Let's see if we can get that issue
straightened out. I think I will send Onset a message and I hope they do
not get besieged with similar ones.

> It is possible to use waste heat from the fire to preheat and dry out more
> fuelwood and if it is worth it, we can do that systematically.

I think this is a really good idea. I have heard that people do that in
some parts. Thanks for the reminder that the stove-fuel-cooking can be a
system with more parts than a combustion box and longer timescales than
dinner!

Last: Bryan mentioned the need for calibration. Yes we need this, but as
cal kits often run into the several hundreds of dollars, what shall we do?
I can't think of a better idea than having a central calibration station
where sensors get returned every year. The shipping would be much cheaper
than the certified cal gas and much less training would be required.
Ideas??

Tami



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